All of the books you’ve mentioned were originally written in languages other than English. If you’re reading them in translation it might help to find versions that have been translated recently (within the last 40 years or so) rather than old translations from the 19th century. New translations, even of old works, tend to be more accessible and have language that feels more natural. That said, writing styles were different in those days so it’s never going to feel like reading a contemporary work, and authors like Nietzsche are even more difficult - reading philosophy books is always a struggle.

Read slowly. Think about what you’re reading and try to make sense of it paragraph by paragraph. Use a dictionary for unfamiliar words. Try to find a quiet place to read with no distractions and try to give yourself as much uninterrupted reading time as possible. If you adjust your expectations and put in the effort I’m sure it will be rewarded. Notre-Dame in particular is really engrossing once you become accustomed to its style - Hugo created a whole world in microcosm full of drama and colorful characters and historical detail, and his discursive style where he goes off on philosophical or historical tangents is all part of it - he’s not just telling a story (for that you can watch one of the movie versions) he’s immersing you in another time.